This invention relates to the field of fuel control systems for fuel cells. More particularly, this invention relates to a fuel control system in which the fuel processor is isolated from the fuel cell by a pressure responsive valve which regulates the flow of fuel forming constituents in proportion to load demands on the fuel cell; and the system also functions to supply fuel as needed to maintain the desired temperature of the fuel reactor.
A fuel cell is a demand system in which the cell operates in response to the load imposed across the cell. Generally, a hydrogen based fuel is used as the fuel supply for the fuel cell, and the hydrogen based fuel is passed through a fuel processor to convert the fuel to pure hydrogen which is then supplied to the fuel cell. In typical prior art systems, the DC load on the fuel cell is sensed and hydrogen and oxygen are delivered to the fuel cell to meet the demand on the cell. Excess hydrogen is delivered from the fuel cell exhaust to the reformer burner of the fuel processor, and the temperature of the reformer is maintained at a desired level by varying the amount of hydrogen delivered to the fuel cell. Such systems operate on the premise that maintaining a constant temperature in the reformer will assure proper fuel supply to the fuel cell to meet the demand. Such systems are generally known as "load following" systems.
The problem with load following systems is that the response time of the fuel cell to change in load is almost instantaneous, whereas the response time of the processor and the flow of materials to the processor and from the processor to the fuel cell is not fast enough to meet the changing load requirements on the fuel cell. Thus, while the response time of the fuel cell to load changes is nearly instantaneous, there is a fixed minimum time delay in the response of the processor and in supplying fuels to the system. Accordingly, as is well known in the art, a time delay is encountered in the response of the processor to the demands of the fuel cell, and this time delay can pose serious operating problems.
Several attempts have been made in the prior art to improve the performance of fuel cells. The patents to Titterington et al U.S. Pat. Nos. 3,098,768, Salathe 3,159,506, Sederquist et al 3,585,078 and Keating 3,607,419 show examples of prior art attempts to control fuel flow in a fuel cell system. However, all of these prior art systems have been less than adequate in meeting the problem for various reasons.